Question & answer
Audience submits and up/down votes each other's responses.
People in the audience submit responses and up/downvote each others responses. The more important issues float to the top allowing the presenter to tackle the most important issues.
More types of activities
Visualize words from audience comments, questions, and thoughts as a word cloud.
Quantify how people feel about an issue on a scale from 1 to 5.
Ask questions before or after an event that people can answer at their own pace.